Burner and process for in situ combustion



Nov. 28, 1961 A. R. SCHLEICHER BURNER AND PROCESS FOR IN snu COMBUSTION Filed Nov. 18, 1957 FUEL AND AIR INVENTOR A. R. SCHLEICHER A TTORNEVS 'an improved process and means United States Patent 3,010,516 BURNER AND PROCESS FOR IN SITU COMBUSTION Arthur R. Schleicher, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Nov. 18, 1957, Ser. No. 697,150 Claims. (Cl. 166-59) This invention relates to a means and process for initiating in situ combustion in a carbonaceous stratum to recover hydrocarbons therefrom.

The recovery of hydrocarbons from underground strata containing carbonaceous material by in situ combustion is becoming increasingly important in the petroleum industry. In this type of recovery in situ combustion in established in a carbonaceous stratum by some suitable means and the combustion zone is driven thru the stratum by direct air injection thru the ignition borehole or by inverse air injection from surrounding boreholes. In either case, the combustion of part of the carbonaceous deposit drives hydrocarbons out of the formation and they are recovered either thru the ignition well,

when utilizing inverse air injection, or thru surrounding production wells, when utilizing direct air injection.

One of the problems involved in this type of recovery is the difficulty encountered in initiating in situ combustion and establishing sufiicient combustion zone to permit driving the combustion zone thru the stratum to produce hydrocarbons therefrom. In order to establish in situ combustion in a carbonaceous formation, it is essential to heat up a substantial area or section around an ignition borehole and, due to the heat loss to the carbonaceous stratum and to the adjacent overburden and underburden, a considerable period is required for heating up the formation preparatory to initiating combustion there- 'in. If too rapid heating with flame type combustion is utilized in the ignition borehole, there is danger of sintering the formation and reducing the permeability thereof so that it is difiicult to inject gas into the formation at sufficient rates to establish and feed a combustion zone.

Accordingly, it is an object of the invention to provide for initiating in situ combustion in a carbonaceous stratum. Another object is to provide a novel flameless type burner for heating purposes. A further object is to provide a method of initiating in situ combustion in a carbonaceous stratum utilizing flameless combustion. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

The burner of the invention comprises a porous refractory hollow body having inlet conduit means for introducing a fuel and oxygencontaining gas into the cavity of the body with no outlet for gases except the pores of the body. A preferred form of the flameless burner is a porous thick-walled refractory tube closed at one end and having inlet means in the other end for introducing a combustible mixture of gases. In another embodiment, the porous burner comprises an annular porous bed of particulate material packed around a perforate well tubing which extends to the surface for injection of air and fuel into the burner located in the carbonaceous stratum to be ignited. The particulate material in the bed may comprise silica, alumina, Alundum (alpha alumina), firebrick, and other suitable refractory materials which may be in the form of small pebbles or irregularly shaped pieces produced by crushing or other means.

The broad process of initiating combustion in a permeable carbonaceous stratum comprises placing a porous refractory burner in an ignition borehole adjacent the carbonaceous stratum, injecting a combustible mixture into the burner and burning the mixture Within the pores ice of the burner so as to heat the same to incandescence by flameless combustion, continuing the burning step so as to heat the stratum adjacent the borehole to incandescence, and thereafter contacting the incandescent stratum with free oxygen-containing gas such as air so as to ignite the carbonaceous material in the stratum. After ignition and establishment of a substantial combustion zone in the carbonaceous stratum the same may be expanded and driven thru the formation by either inverse or direct air injection.

A more complete understanding of the invention may be obtained by reference to the accompanying schematic drawing of which FlGURE 1 is an elevation thru a carbonaceous stratum showing an arrangement of apparatus for igniting same; and FIGURE 2 is a similar elevation showing another embodiment of the invention for igniting a carbonaceous stratum and for advancing the burning zone by inverse air injection.

Referring to FIGURE 1, a borehole 10 penetrates a carbonaceous stratum 12 and is provided with casing 14 extending substantially to the carbonaceous stratum. Tubing string 16 connects with a fuel and air line 18 above the well head and with porous burner 20 within formation 12. Burner 20 must be of lesser diameter than the internal diameter of casing 14 so that it may be lowered into the carbonaceous stratum thru the casing. Conduit 19 provides a vent for combustion gas and/or hydrocarbons during certain stages of the process. A spark plug or similar igniting device 22 is positioned in the upper end of burner 20 and is ground to tubing string 16. An insulated conductor 24 connects the other terminal of the spark plug to a current source 26 at the surface and this source is grounded by means of conductor 28 to tubing 16.

Referring to FIGURE 2, the ignition borehole 10 is provided with a porous burner 30 which is formed in stratum 12 around a perforate pipe or tube 32 and this tube is connected by a pair of conduits 34 and 36 leading thru the well head to conduits 38 and 40, respectively, and adapted to inject fuel and air into perforate tube 32 for dispersion into the porous annulus of burner 30. An ignition device 41 is positioned in the annular wall of burner 30 for the purpose of igniting the combustible mixture fed thereto. This ignition device -is shown in the form of a heating coil imbedded in the casing 42 just below the well head and a vent line 45 allows gases to escape to recovery means during cer-' tain phases of operation.

Operation in accordance with the invention comprises injecting a mixture of fuel and air into burner 20 (or 30) and igniting the mixture so as to burn the same by flameless combustion. In burner 20 the mixture is ignited as it emerges from the porous wall of the burner and the mixture burns on the surface of the burner until the particles in the outer layer of the burner become incandescent; combustion then takes place in the pores of the burner without flame outside of the burner itself. In burner 30 the electric heater or coil 41 becomes incandescent with flow of current therethru and the combustible mixture is ignited and burns by flame less combustion around the incandescent wires. As combustion is continued, the particles of the porous burner carbonaceous material therein.

gas ratio was :1 (stoichiometric value).

become incandescent throughout and the heat developed therein is transmitted to the adjacent stratum 12.

Upon continuation of the combustion process in flameless burner 20 or 30 the adjacent stratum becomes heated to 'incandescence to a substantial depth around the burner and is ready for the ignition step. At this time the incandescent stratum is contacted with free oxygen, either by direct or by inverse injection of a free-oxygencontaining gas, such as air. In utilizing the apparatus of FIGURE 1, it is feasible to gradually increase the proportion of air in the injected mixture or to cut oif the supply of fuel gradually or abruptly so that free oxygen contacts the incandescent stratum and ignites the hot The combustion gas formed in the borehole during heating up of the same, utilizing the device of FIGURE 1, can be removed either thru vent 19 or thru stratum 12 to one or more surrounding boreholes therein. When operating, utilizing the arrangement of apparatus of FIGURE 2, combustion gas is driven thru the formation to borehole 42 during the heating up stage of the ignition process and is vented thru conduit 45. When a section of the stratum around burner 30 suflicient to provide a self-propagating combustion zone when heated to elevated temperature, has been heated to incandescence, the flow of air and fuel into burner 30 is cut off and air is injected thru conduit 44 from which it passes thru borehole 42 and stratum 12 to the combustion zone around borehole 10. When air and fuel are cut off to the ignition borehole 10 and inverse air is introduced thru 44, the and fuel injection tubing 40 and 38 are replaced with a production string and fluid hydrocarbons passing from the formation to the ignition borehole (which now becomes a production borehole) are removed by conventional recovery methods.

To illustrate the burner of FIGURE 2, tests were made in a 43 mm. internal diameter Vycor glass tube with a vertical packed column of Alundum spheres inch in diameter and forming an 8 inch column. An airnatural gas mixture flowing thru the pebble column was ignited and the fuel-air flow adjusted until the flame was on the top layer of pebbles. At this point the air- When the temperature of the top layer of pebbles reached approximately 1000 F. the flame moved into the interstices in the upper layers of pebbles and shortly thereafter the combustion became a flameless hot zone within the pebble bed. After becoming flameless, the combustion zone moved slowly down the column of pebbles becoming more diffused. During this stage, maximum temperatures were about 1650 F. with an air-gas ratio of 12:1 and a total flow rate of approximately 50 s.c.f.h. The combustion zone proceeded at about 2 inches per hour and when the combustion zone reached the middle of the column, the air-fuel input was increased to the maximum permit-ted by the air source with an air-gas ratio of 15:1,the pebbles in the combustion zone reaches a temperature of 2585 F. The recorded temperatures were measured by an optical pyrometer.

To illustrate the burner of FIGURE 1, a burner was made from an Alundum rod by drilling an axial cavity therein. Air and propane were injected into the Alundum tube and the combustible mixture was ignited as it emerged from the surface pores of the tube. Initial combustion occurred as a flame on the outer surface of the burner but as the Alundum reached 'dull red heat, the flame disappeared, and flameless combustion took place within the pores of the Alundum so that the entire mass of Alundum became incandescent. The temperatures of this Alundum burner approximated those of the packed column burner.

Certainmodifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for initiating in situ combustion in a permeable carbonaceous stratum comprising disposing a porous refractory burner in an ignition borehole adjacent said stratum; injecting a combustible gaseous mixture into said burner and igniting and burning said mixture within the pores thereof by flameless combustion so as to heat said burner to incandescence; continuing said burning by flameless combustion so as to heat said stratum adjacent said borehole to incandescence whereby said burning by flameless combustion avoids impingement of flame on the wall of said borehole; and thereafter contacting the incandescent stratum with free oxygen so as to initiate combustion of the carbonaceous material therein.

2. The process of claim 1 wherein said oxygen is passed to said incandescent stratum thru said stratum from at least one other borehole therein so as to advance the incandescent or combustion zone radially outward from the ignition borehole.

3. The process of claim 1 wherein said oxygen is injected into said incandescent stratum thru said ignition borehole to initiate said combustion and to expand the resulting combustion zone; and oxygen is then passed to the expanded combustion zone thru said stratum from at least one other borehole therein.

4. In combination in a borehole penetrating a combustible carbonaceous stratum, a perforate tube Within said borehole and said stratum; a packed bed of particulate refractory solids forming an annulus around said tube, the periphery of said bed being in contact with said stratum; means for injecting fuel and free-oxygen-containing gas thru said tube into said bed; and heating means extending vertically substantially from the bottom to the top of said bed for raising the temperature thereof to incandescence to ignite the injected fueloxygen mixture, whereby said fuel is burned by flameless combustion without impingement of flame on the wall of said borehole.

5. The combination of claim 4 wherein said packet bed is coextensive vertically with said stratum and said heating means comprises a helical electrical resistance coil imbedded in said packed bed from top to bottom thereof.

6. The combination of claim 4 wherein said refractory solids comprise small substantially spherical pebbles.

7. The combination of claim 4 wherein said refractory solids comprise small substantially spherical alumina.

8. A process for packing an igniting means in a bore- .hole and initiating in situ combustion in a carbonaceous stratum penetrated by said borehole which comprises positioning axially in said borehole within said stratum a perforate tube on the lower end of conduit means for supplying fuel and air to said tube; positioning a helical electric heating coil in the annulus formed between said tube and the wall of said borehole spaced from said tube and extending substantially from the top to the bottom of said tube; thereafter packing said annulus around said coil and said tube with a bed of particulate refractory solids; electrically heating said coil to incandescence; injecting a combustible gaseous mixture of 'fuel and air thru said tube into said bed so as to contact free-O is effected by increasing the ratio of O to fuel in said mixture.

10. Burner apparatus for use in a borehole penetrating a combustible carbonaceous stratum comprising a tubing string in said borehole extending to said stratum; a permeable refractory relatively thick-walled hollow burner body attached to the lower end of said tubing string so as to feed gas into said hollow body, the only outlet from said hollow body being thru fine pores in the wall thereof; and means outside of said burner body for igniting a combustible gaseous mixture fed thru said tubing string into said hollow burner body and thru the pores of said wall, whereby ignition of said combustible mixture on the surface of said burner body wall heats said surface to incandescence so that said combustible mixture burns with-in said pores in said well by fiameless combustion.

References Cited in the file of this patent UNITED STATES PATENTS 

